1. Field of the Invention
The present invention relates to a method of preparing silicon nitride from silica.
2. Description of the Prior Art
Sintered silicon nitride has been used to manufacture articles which are subjected to high temperatures and high stresses. The thermal and mechanical properties of the sintered silicon nitride are greatly affected by the nature of the starting materials used to prepare it. It is preferable that the silicon nitride contain as much .alpha.-Si.sub.3 N.sub.4 powder as possible.
Silicon nitride powder has been prepared by the following methods:
1. The reaction of nitrogen and silicon;
2. The vapor phase reaction of silicon tetrachloride or silane with ammonia; and
3. The nitridization of purified silica with carbon powder.
Each of these methods has deficiencies. Method (1) requires silicon metal which is expensive and consequently, the silicon nitride produced is also expensive. Method (2) cannot be used for the mass production of inorganic refractory raw material, while Method (3) requires a long reaction time at elevated temperatures. Moreover, the yield of .alpha.-Si.sub.3 N.sub.4 is low.
A need continues to exist for a process of preparing silicon nitride, especially for a process which produces a high yield of .alpha.-Si.sub.3 N.sub.4.